Silicon-based light emitting diodes, for example, near infrared, visible, and ultraviolet light emitting diodes using silicon nano-size dots, have new structures to overcome the limits of a conventional silicon semiconductor that provides low luminous efficiency due to indirect transition. Silicon-based light emitting diodes are compatible with other silicon-based photoelectronic devices and manufactured with low costs. Hence, many researches into silicon-based light emitting diodes have been made. However, because silicon-based light emitting diodes still provide low luminous efficiency, it is difficult to apply the silicon-based light emitting diodes to electronic apparatuses, etc., and many improvements are needed.
The formation and characteristics of a crystalline silicon nano-size dot usually used in silicon-based light emitting diodes are disclosed in Appl. Phys. Lett. 85, 5355 2004. The structure and radiation characteristics of silicon-based light emitting diodes are disclosed in Appl. Phys. Lett. 86, 071909 2005.
One of the essential causes of a degradation of the luminous efficiency of silicon-based light emitting diodes is that all emitted light cannot be utilized overall. In other words, silicon-based light emitting diodes using silicon nano-size dots use a silicon substrate and accordingly utilize only light heading for the upper surface of the silicon substrate among lights emitted in all directions. In other words, light heading for the lateral surfaces of the silicon substrate are not used and lost. Therefore, silicon-based light emitting diodes provide relatively lower luminous efficiency than compound semiconductor light emitting diodes.